Overall Description
Column
This webpage is a summary of my Bachelor of Engineering Thesis.
If you would like to see plots, just go to the next page. Otherwise, this is a short introduction so this can be understood in a glimpse.
The point of my thesis was to build a magnetic field sensors that uses an optical fibre. This was accomplished by building different types of interferometers, with ferrofluid reacting with magnetic field.
The sensor with a ferrofluid-filled capillary described in this paper has not been previously described in literature, or I couldn’t find any.
Interference:
When two waves of light meet each other, and their lengths match, they can add or subtract from each other. This is called interference. This act will be used to detect changes in optical properties of a fluid - which is dependent on the magnetic field. The interference can also happen for a whole range of wavelengths a the same time. In our case, the light can interfere when it is inside of a capillary.
Used items:
A cappilary, or “no core fibre” is just a tiny and very thin glass tube. It has a small hole inside, and we can put a liquid inside of it.
A ferrofluid is a fluid, filled with tiny particles that react with magnetic field. That way, we can change the most important property - the angle by which light gets reflected - using magnetic field. In my study, I tested two ferrofluids made by Ferrotec company.
Unfortunately the lasers that I have used are not to be seen by human eye. Fortunately, I can still shine red light through elements that I’ve build.
Column
The princible - summing up:
By placing a cappilary in a ferrofluid, we can alter its optical property using magnetic field. That way, and adding that each wavelength refracts at a slightly different angle, we can measure changes of the amount of light that gets through our measuring element.
Type I
Column
Whole range of wavelengths, each next series have greater magnetic induction:
Above plot, zoomed at the area of interest:
Column
Basic schema for how the sensor works:
As the magnetic induction changes, the each wavelengths refracts at slighly different angle